Giant thermal expansion of a two-dimensional supramolecular network triggered by alkyl chain motion

Abstract

Thermal expansion, the response in shape, area or volume of a solid with heat, is usually large in molecular materials compared to their inorganic counterparts. Resulting from the intrinsic molecule flexibility, conformational changes or variable intermolecular interactions, the exact interplay between these mechanisms is however poorly understood down to the molecular level. Here, we investigate the structural variations of a two-dimensional supramolecular network on Au(111) consisting of shape persistent polyphenylene molecules equipped with peripheral dodecyl chains. By comparing high-resolution scanning probe microscopy and molecular dynamics simulations obtained at 5 and 300 K, we determine the thermal expansion coefficient of the assembly of 980 ± 110 × 10 −6 K −1 , twice larger than other molecular systems hitherto reported in the literature, and two orders of magnitude larger than conventional materials. This giant positive expansion originates from the increased mobility of the dodecyl chains with temperature that determine the intermolecular interactions and the network spacing.

Synthesis of Giant Dendritic Polyphenylenes with 366 and 546 Carbon Atoms and Their High‐vacuum Electrospray Deposition

“…Importantly, the corresponding precursor is generally deposited onto metal substrates under UHV conditions by sublimation, which cannot be achieved for high‐molecular‐weight precursors like large dendritic PPs. To this end, HV‐ESD allows deposition of macromolecules onto substrates without the need of thermal evaporation [35–40] . Thus, we attempted the deposition of both dendritic PPs 3 and 4 onto Au(111) surface by the HV‐ESD technique (see supporting information for details).…”

Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene

“…Many two-dimensional (2D) materials have excellent optical, mechanical, electromagnetic, and other attractive physical properties [1,2]. Their structures can be usually tailored or modified at the nanoscale [3,4]. One type of modification is the fabrication of 2D layered heterostructures, which have been the subject of intensive scientific research in recent years [5][6][7].…”

Influence of electrospray deposition on C60 molecular assemblies

“…We show the influence of HV-ESD on the surface preparation of molecular layers. This method is known to be a good alternative to TE when working with non-volatile molecules and has proven to be compatible with sensitive techniques, such as low-temperature AFM with CO tip imaging [10,12]. Nevertheless, we have shown some influence on the surfaces and the formation of molecular assemblies that should not be neglected when studying molecular structures, especially, when no post-deposition treatment is carried out.…”

“…Based on electrospray ionisation [4], HV-ESD gives the possibility to study complex or fragile molecules that are impossible to safely deposit onto surfaces with traditional deposition techniques. So far, using HV-ESD, numerous molecular species with potential applications in biology and photovoltaics, or with magnetic or thermal expansion properties have been deposited on a variety of materials, ranging from metal surfaces [5][6][7][8][9][10][11][12][13], over metal oxides [14] and insulating substrates [15] to graphene monolayers on metals [16]. In HV-ESD-based devices, a solution containing the molecules reaches an emitter located in front of the entrance capillary, as shown in Figure 1a.…”

“…In such a situation, all species introduced in the vacuum that are not evacuated via the pumping system or adsorbed to a wall of the device can reach the sample. Nevertheless, the contamination from solvent introduction can be reduced down to conditions compatible with high-resolution scanning probe microscopy (SPM) techniques [10,12]. Buckminsterfullerene C 60 , scheme in Figure 1b, is among the most extensively studied molecules in surface science, especially in SPM under UHV conditions.…”